A、A middle-aged woman with chronic lung problems. B、An elderly man who has chronic heart problems. C、A newly-born infant who is

Influenza, or the flu, attacks up to one billion people annually. In the US, it kills 20,000 annually, most of whom are children or elderly. Occasionally the flu becomes pandemic: in 1918, it killed 20 million people worldwide. (32)The flu is a kind of infection which spreads through the air by coughing, sneezing, or simply talking. It is not caused by getting caught in a rainstorm or by sleeping with the fan or air-conditioning on.
     (33)It doesn’t sneak up on you for the first few days, like a cold does. All of a sudden, you feel weak, you have a high fever, you have chills, yon cough frequently and forcefully, your throat is sore, and your body aches.
     For most adults, the treatment is to simply wait it out: stay home, get lots of bed rest, drink lots of fluids, and take over-the-counter medications such as aspirin and pain-killers. Symptoms usually go away within two weeks. (34) For the elderly and young, it may become a bacterial infection with deadly consequences, because the victim becomes too weak to battle the disease. The death rate for the general population is about one in 1,000. (34) Those most susceptible to severe effects of the flu are people over 65 and people with chronic heart or lung problems.
     Flu season in the US is usually from December to March. (35)The best prevention, of course, is to stay away from infected people. Since that is almost impossible, the next best preventive strategy is to get an annual flu shot. This vaccine reduces the number of people who get infected -- and who die -- yearly.